Effect of direct reduced iron on oxygen distribution between slag and bath in electric arc furnaces

Test charges containing 40 to 95% direct reduced iron (DRI) were melted in two identical electric arc furnaces. Slag and the corresponding metal samples were collected from the furnace in the course of the steelmaking process and from the ladle after deoxidation and composition adjustment. The temperature was measured just before sampling. The activity coefficient and activity of total ferrous oxide in the slag were determined by using the theory of regular ionic solutions. The activity was used to assess the oxygen concentration in the metal. The effect of slag composition on FetO activity coefficient and activity was investigated. The enthalpy of solution of total ferrous oxide in the slag was found to be 78 kJmol(-1). The ratio of activity to concentration of FetO is equal to 0.0138. The effects of DRI proportion and degree of metallization on a(FetO) were investigated. The activity coefficients of oxygen and carbon in the bath are 0.7243 and 1.0825, respectively. The activity coefficient and activity of oxygen in the metal decrease with increasing carbon concentration, carbon activity coefficient and activity. An "oxide capacity" has been developed which does not need the use of a(FetO). It correlates strongly with temperature over the range from 1500 to 1670 degrees C. The basicity has only a small influence compared with the large temperature effect. The oxide capacity increases with growing DRI proportion and decreases with increasing metallization between 93.43 and 95.25%. Oxygen distribution between slag and metal was assessed by using the oxide capacity. Calculated values compare well with the corresponding data obtained from slag and metal analyses. The oxide capacity can be used in monitoring the steelmaking operation.